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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        'use strict';
        var num = 10;
        console.log(num);
        //不能随意删除已经声明好了的变量
        //delete num;
        function fn() {
            console.log(this);
        }
        fn();

        function Star() {
            this.sex = '男';
        }
        var star = new Star();
        console.log(star.sex);
        setTimeout(function() {
            console.log(this);
        }, 1000)
    </script>
</body>

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